1. Field of the Invention
The present invention relates to a method of effectively preventing polymer scale from sticking, and particularly to a method of preventing polymer scale from sticking in a polymerization vessel during the polymerization of monomers having an ethylenically double bond.
2. Description of the Prior Art
In processes of preparing polymers by polymerizing monomers in a polymerization vessel, known to arise is the problem that the polymer sticks on inner wall surface and so forth of the polymerization vessel in the form of scale. Once the scale of polymer sticks on the inner wall surface and so forth of the polymerization vessel, much labor and time are required as a result to remove the scale of polymers. Disadvantages may also result such that the yield of polymers and the cooling capacity of the polymerization vessel are lowered, and the sticked scale of polymers may peel from the surfaces to mix into a product, and the quality of manufactured polymers are thereby made poor.
As methods of preventing polymer scale from sticking on the inner wall surface and so forth of a polymerization vessel, there have been hitherto proposed, for example, a method in which a polar compound, a dye, a pigment or the like is coated on the inner wall surface (Japanese Patent Publication (KOKOKU) Nos. 30343/1970 and 30835/1970), a method in which an aromatic amine compound is coated (Japanese Pre-examination Patent Publication (KOKAI) No. 50887/1976), and a method in which a reaction product of a phenolic compound with an aromatic aldehyde is coated (Japanese Pre-examination Patent Publication (KOKAI) No. 54317/1980).
These are effective in preventing polymer scale from sticking, when vinyl halide monomers such as vinyl chloride or monomer mixtures mainly comprised of said monomers and containing a small amount of monomers copolymerizable therewith are polymerized.
However, in instances in which the monomers to be polymerized comprise other monomers having an ethylenically double bond such as styrene, alpha-methylstyrene, acrylate and acrylonitrile, these monomers have so large a dissolving power against the coating formed by the above sticking-preventing methods that part or the whole of the coating may be dissolved away, so that it becomes impossible to effectively prevent polymer scale from sticking on the inner wall surface and so forth of a polymerization vessel. This sticking of scale particularly tends to occur when the polymerization vessel is made of stainless steel.